Multiple-completion geothermal energy production systems

Abstract

A system for the mining of geothermal energy in which a plurality of geothermal wells radiate from a single surface site into a subsurface geothermal reservoir. The wells can be drilled by conventional slant drilling techniques and each may contain a closed end heat exchanger which receives water and generates steam. Some of the heat exchangers are disposed vertically and others are implanted horizontally. By alternating production of the wells in a programmed cyclical manner, convective movement of the hydrothermal fluid will occur within the geothermal zone. The generated steam is collected in a reservoir at the surface site and utilized to generate electricity. The condensate from the turbine can be recycled to the wells.

What is claimed is: 
     
       1. A system for the recovery of geothermal energy comprising: a closed, steam vapor collection reservoir vessel having side walls, a top wall and a bottom wall, said side walls and bottom wall being recessed below the surface of the earth and said bottom wall containing a plurality of apertures;   a plurality of cased geothermal wells, the casings of each having a first end converging toward and sealingly connected to one of the apertures in the bottom wall of said reservoir and each well casing diverging from said reservoir and having a second end disposed within a common, wet geothermal zone having a temperature of at least 300° F;   said second ends being closed and a portion of each well within the zone and containing the closed end forming a heat exchanger;   supply means for delivering water from the surface to said heat exchanger to form steam vapor therein; and   vapor fluid delivery means within each of said wells to conduct heated steam vapor fluid from each second end to said reservoir.   
     
     
       2. A system according to claim 1 further including valve means connected to each of said wells for terminating delivery of water to said reservoir. 
     
     
       3. A system according to claim 2 further including control means associated with said valve means for cycling production of said well means. 
     
     
       4. A system according to claim 1 in which at least one of said common ends terminates in a different horizontal plane within said zone than other of said second ends. 
     
     
       5. A system according to claim 1 in which said wells are lined with a metal casing and a cement outer casing. 
     
     
       6. A system according to claim 5 in which at least a portion of the metal casing within said zone is not cased with cement. 
     
     
       7. A system according to claim 1 in which said geothermal zone is absent geothermal fluid and further including water injection wells extending from the surface into said common zone and having lower ends terminating in the vicinity of the second ends of the geothermal wells and pump means for injecting water into said injection wells. 
     
     
       8. A system according to claim 6 in which the second end of each of said wells includes a closed heat exchanger and a central water delivery pipe is disposed within the well and connected to said heat exchanger. 
     
     
       9. A system according to claim 8 in which an annular water supply loop is disposed adjacent the first ends of said heat exchangers and connection means sealingly penetrating the wall of each heat exchanger connecting said loop to each central delivery pipe. 
     
     
       10. A system according to claim 9 further including separate valve means connected to each connection means for controlling the delivery of water to each of said wells. 
     
     
       11. A system according to claim 1 in which said second ends includes a closed end metal heat exchanger having metal walls directly exposed to the geothermal zone. 
     
     
       12. A system according to claim 1 in which a plurality of said heat exchangers are implanted horizontally in said zone and a plurality are implanted vertically in said zone. 
     
     
       13. A system according to claim 1 in which said zone is at least 3000 feet below the surface and has a temperature of at least 300° F. 
     
     
       14. A system according to claim 1 in which said reservoir walls are dormed of metal and the side metal walls are cased with cement. 
     
     
       15. A method of recovering geothermal energy comprising the steps of: recessing the apertured bottom wall and the side walls of a closed, steam vapor collection reservoir vessel below the surface of the earth;   slant drilling a plurality of geothermal wells, each having a first upper end converging toward said reservoir vessel and a second lower end disposed within a common, wet geothermal zone;   casing each of said wells;   connecting each of the upper, first ends of said casings to the aperture in the bottom wall of said reservoir vessel;   inserting a closed end heat exchanger at said second end;   injecting water into each of said heat exchanger; and   delivering heated water vapor from each exchanger to the reservoir.   
     
     
       16. A method according to claim 15 in which at least one of said heat exchangers is implanted horizontally within said zone and at least one heat exchanger is implanted vertically within said zone. 
     
     
       17. A method according to claim 16 further including the step of implanting at least one of said heat exchangers at a different horizontal plane within said zone than said other heat exchangers. 
     
     
       18. A method according to claim 15 in which said heat exchanger has an outer metal shell directly exposed to said geothermal zone. 
     
     
       19. A method according to claim 15 in which said zone is dry, and further including the step of injecting water into said zone. 
     
     
       20. A method according to claim 15 further including the step of inducing convective movement of hydrothermal fluid within said zone by cycling production of heated fluid delivery to said reservoir among said wells.